Operation MO and the Battle of the Coral Sea

Last updated 05:00 05/05/2012

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May 5 marks 70 years since the Battle of the Coral Sea was fought to the east of North Queensland during May 1942. This extensive and complex battle has over time acquired the status of a great allied naval victory. This claim is certainly debatable.

At the time the Coral Sea was the largest naval battle fought in the Pacific since Tsushima in 1905 but within a month it had been overshadowed by the United States Navy's stunning victory at Midway. A review of this important battle is now appropriate.

The Battle of the Coral Sea was the first fleet action to be fought by aircraft carriers rather than battleships. When Vice Admiral Nagumo's force attacked Pearl Harbor, the Imperial Japanese Navy had 10 carriers in service with a further two nearing completion.

To counter this force, the US Navy had seven carriers plus one escort carrier available. The disparity between these forces was even more marked with the two smallest US carriers, Ranger and Wasp, allocated to the Atlantic Fleet and only the five largest carriers of the Saratoga and Yorktown classes designated to serve in the Pacific.

This disparity widened further when on January 10, 1942, the Saratoga was torpedoed by the Japanese submarine I-6, putting the carrier out of action for five months and crucially not available for the Coral Sea and Midway battles.

By April 1942, having swept all before them, the Japanese were planning the extension of their defensive perimeter. In the south, this included the capture of Port Moresby, Tulagi in the Solomon Islands, New Caledonia, Fiji and Samoa. This would then cut the lines of communication from the United States, isolating Australia and New Zealand. These plans were rapidly progressed when on 18 April, American B25 bombers under the command of Lieutenant Colonel James Doolittle attacked Tokyo. These medium bombers had been flown off the carrier Hornet which was operating with its sister ship Enterprise under the command of Vice Admiral Halsey as Task Force 16 (TF16).

The capture of Port Moresby and Tulagi plus the occupation of Nauru and Ocean Islands, designated Operation MO, was planned for early May with Operation MI, the invasion of Midway, and Operation AL, the capture of the western Aleutian islands of Attu and Kiska, scheduled to take place simultaneously a month later. A strong response from the US Navy was anticipated and almost the entire Japanese fleet was committed, with three carriers for Operation MO, six carriers for Operation MI and two carriers for Operation AL.

The Japanese had three strategic objectives and the Battle of the Coral Sea was to be fought in three distinct phases in relation to these objectives. The first objective was to seize Tulagi, the administrative centre of the Solomon Islands, and to establish a seaplane base. Aircraft from this base would then monitor allied naval movements in the Coral Sea and protect the southern flank of the Port Moresby invasion force. The second but primary objective was to capture Port Moresby which would then provide a base to mount attacks on northern Australia. The third objective was to occupy Nauru and Ocean Islands which, with their phosphate deposits, had some strategic significance.

This complex operation necessitated the use of a number of naval groups to achieve the three objectives. In overall command was Vice Admiral Inouye at Rabaul and his force was comprised as follows:

"Tulagi Invasion Group: Rear Admiral Shima in the cruiser/minelayer Okinoshima with one transport, one seaplane transport, two destroyers, two submarine chasers and five minesweepers. This group was tasked with seizing Nauru and Ocean Islands following the Tulagi invasion "Port Moresby Invasion Group: Rear Admiral Abe with eleven transports. carrying some 6,000 troops with an escort of a minelayer and four minesweepers. Accompanying this group was an Attack Force commanded by Rear Admiral Kajioka in the light cruiser Yubari with six destroyers.

"Support Group: Rear Admiral Marushige with the light cruisers Tatsuta and Tenryu, a seaplane transport and three gunboats. After providing support for the Tulagi invasion, this group was to establish a seaplane base in the Louisiade Archipelago.

"Covering Group: Rear Admiral Goto with the light carrier Shoho, the heavy cruisers Aoba, Kako, Kinugasa and Furutaka plus a destroyer and an oiler. This group was to provide cover for both the Tulagi and Port Moresby invasion forces. "Carrier Striking Force: Rear Admiral Hara in the carrier Zuikaku together with sister carrier Shokaku. In overall command Vice Admiral Takagi in the heavy cruiser Myoko together with heavy cruiser Haguro, six destroyers and an oiler. This group was to provide long range cover by intercepting and destroying Allied warships. "Submarine Force: Captain Ishizaki with four large I type submarines stationed southwest of Guadalcanal and two medium RO type boats off Port Moresby. "Land Based Aircraft: Rear Admiral Yamada commanding 25th Air Flotilla operating out of Japanese held airfields together with the aircraft to be operated out of the new seaplane bases at Tulagi and the Louisiade Archipelago.

The Allied Response

Japanese signal traffic was being intercepted and decoded at the joint USN/RAN intelligence united known as Fleet Radio Unit Melbourne (FRUMEL). With the information provided by FRUMEL, the Allies were able to concentrate three task forces in the Coral Sea under the command of Rear Admiral Fletcher USN as follows:

In support of TF17 but under the overall command of General Douglas MacArthur were:

"Eastern Australian Submarine Group: Captain Christie USN recently arrived at Brisbane from Panama with tender Griffin and seven elderly S Class submarines. Of these one was in the Gulf of Papua and three were patrolling in the area of St. George's Channel between New Britain and New Ireland. "Allied Air Forces: Lieutenant General Brett USAAF with allied aircraft based in Australia and New Guinea.

Following the "Doolittle Raid" on Tokyo, TF16 under the command of Vice Admiral Halsey returned to Pearl Harbor in late April. Halsey's two carriers were quickly refueled and replenished then sailed on 30 April to reinforce Fletcher in the Coral Sea. However, they could not arrive there at the earliest until mid May.

Under the direct command of Admiral Nimitz, Commander in Chief in the Pacific (CINCPAC), was Task Group 12.2 (TG12.2) comprising the Royal New Zealand Navy light cruisers Achilles and Leander plus three US destroyers. On 4 May, unbeknown to the Japanese, TG12.2 escorted five transports into Vila harbour in the New Hebrides group where it then remained to cover the unloading of the transports. While not directly involved in the Coral Sea battle, TG12.2 ships would make a useful contribution at its conclusion.

The Coral Sea battleground was complicated in that it straddled two separate operational commands. The Coral Sea lay in the South West Pacific Area under the control of MacArthur while Fletcher's TF17 reported directly to Nimitz. This demarcation was to have significant implications in relation to intelligence from land based air patrols and the extent of US submarine operations.

First Phase: Tulagi Skirmish

Covered by Goto and Marushige, Shima's invasion group seized Tulagi with little resistance on 3 May. Upon learning of the Japanese landing, Fletcher sped to the north-east with his Yorktown group and was in a position to launch a carrier strike early on the morning of 4 May.

By then, Shima had sailed his transports after unloading and both Goto and Marushige had withdrawn to the north to cover the Rabaul invasion group. The overconfident Japanese were caught without support and in three strikes launched by the Yorktown, the destroyer Kikutsuki, three auxiliary minesweepers; No. 1, No. 2 and Tama Maru plus four landing barges were sunk.

The Okinoshima and two smaller vessels were also damaged. More importantly, all the Japanese seaplanes were destroyed eliminating the Japanese reconnaissance capability which was to have operated out of Tulagi. The American pilots believed that they had inflicted greater damage than actually achieved but the Japanese had certainly received a setback.

After the third strike and the loss of three aircraft, Fletcher withdrew to the south to rendezvous with Fitch and Crace. Shima retired to the north on 5 May, covered by Goto who had reversed course on learning of the American air attack. The landing force remained at Tulagi, leaving a Japanese foothold in the Central Solomons.

Second Phase: The Carrier Battle

After refueling his ships on 5 May Fletcher detached his oilers, each with a destroyer escort, to the south. He then headed north-west for the Louisiade Archipelago to intercept the Japanese invasion force en-route to Port Moresby.

Meanwhile Takagi's Carrier Striking Force had quickly sailed southward to the east of the Solomon Islands and entered the Coral Sea south of San Cristobal Island and behind TF17. Aerial reconnaissance by both the American and Japanese carrier groups on 6 May was unsuccessful due to heavy cloud cover.

Early on the morning of 7 May Fletcher detached Crace (now designated TG17.3) with cruisers Australia, Chicago and Hobart plus destroyers Perkins, Walke and Farragut to cover the Jomard Passage where the Port Moresby invasion force was expected to enter the Coral Sea.

This was a risky decision by Fletcher, an admiral not particularly noted for his boldness. Crace was under no illusion regarding the forces he was facing but was fortunate in that the invasion, support and covering groups were not concentrated. Crace had not proceeded far on what has become known as "Crace's Chase" when his force was detected by a Japanese patrol aircraft. Inouye decided to attack Crace using land based aircraft from Rabaul and unwilling to risk his transports, at 0900 he ordered the Invasion Group to turn about until Crace's force had been destroyed.

Meanwhile Takagi had been conducting air patrols to the south of Fletcher and one of his scouts reported a carrier and a cruiser south-west of Rennell Island. Assuming that this was part of the American carrier force he prepared to launch an all out air attack. The Japanese had in fact located the detached oiler Neosho and its escorting destroyer Sims. It was to take over two hours for the Japanese to overcome the fierce defence put up by the American ships.

Sims was eventually sunk with only 14 survivors and Neosho was badly damaged but still afloat. Believing that the order to abandon ship had been given, 68 men took to the life rafts but the rest of the crew, along with the Sims' survivors, remained on board the crippled oiler.

At 0815 Fletcher received a sighting report of two carriers and four cruisers 235 miles to the north-west. This report was inaccurate as this force was Marushige's Support Group. Fletcher immediately ordered a heavy air strike and was dismayed to learn of the reporting error when the scout plane landed. He decided to proceed with the air strike and was to be rewarded for his gamble.

An American pilot chanced to sight Goto's Covering Group to starboard and this was immediately attacked. The American planes concentrated on the carrier Shoho and this was quickly overwhelmed, sinking at 1135 with the loss of most of the carrier's complement.

This was a significant victory for Fletcher as not only had he had eliminated a threat to his carriers but more importantly he had destroyed the air cover for the Port Moresby Invasion Group.

Crace had been shadowed continuously since being located and his force had mistakenly been reported as comprising two battleships, a heavy cruiser and four destroyers.

Shortly after 1500, when Crace was south of the Jomard Passage, his force was attacked by a dozen twin engined Mitsubishi Nell torpedo bombers. With good seamanship and some luck this attack was beaten off with the loss of five aircraft. No sooner had this attack finished when another group of Nell bombers attacked from astern with bombs.

Although Australia was narrowly missed, TG17.3 remained unscathed. A third attack by another three aircraft which occurred shortly afterwards was later determined to be a case of friendly fire by USAAF B17 heavy bombers. The Japanese pilots who returned to Rabaul reported that they had sunk one battleship and had heavily damaged another battleship plus a cruiser.

This report was taken at face value and a second attack was not ordered. Without any news from Fletcher, Crace turned south until dark and then westward to counter any Japanese advance on Port Moresby.

Having wasted time attacking Neosho and Sims, Takagi decided to launch a late afternoon strike against Fletcher even though he was unsure of TF17's location. This force of 27 aircraft narrowly missed the American carriers due to adverse weather conditions and on reaching the limit of their range they jettisoned their bombs before returning.

The return flight passed close to TF17 and several Japanese aircraft were shot down, some while mistakenly trying to land on the Yorktown. Only six aircraft made it back to the Japanese carriers.

By the end of the day, both Fletcher and Takagi had identified the position of their adversary. On the morning of 8 May, both sides located their opponents almost simultaneously. Shokaku was hit by a number of bombs from Yorktown's aircraft and was unable to operate her aircraft.

Zuikaku was hidden by a rain squall and escaped punishment. Meanwhile, both Lexington and Yorktown were attacked by Takagi's experienced aircrew. Lexington was hit by two torpedoes and at least two bombs while Yorktown was damaged by one bomb but was still able to operate her aircraft.

Shortly after midday Lexington was rocked by a large internal explosion caused up by the build up of petrol fumes from ruptured fuel tanks. This started new fires which gradually spread and at 1707 the order was given to abandon ship. The Lexington was eventually sunk by torpedoes fired by the destroyer Phelps. Fletcher then retired to the south with the damaged but operational Yorktown to await the arrival of Halsey.

Shokaku had been badly damaged and was detached to return to Truk and then back to Japan for repairs. Japanese aircraft losses had been very heavy and Takagi was in no position to renew the attack.

He sought approval from Inouye to retire from the battle zone which was given and at the same time the Port Moresby invasion was finally cancelled.

Combined Fleet Admiral Yamamoto was furious that Fletcher had been allowed to withdraw and ordered Takagi, to be joined by Goto, back into the Coral Sea. Fletcher was long gone and believing that both American carriers had been sunk, Takagi finally left the Coral Sea on 11 May.

On the same day, the destroyer Henley, detached from TG12.2 at Vila, located the now barely floating Neosho. After rescuing 123 survivors, the Neosho was scuttled and the Henley sailed for Brisbane.

Third Phase: Submarine Intervention

Wile the carrier battle raged to the south, Shima had been regrouping his force for the occupation of Nauru and Ocean Islands. This included reinforcements from the now disbanded Port Moresby Invasion Force.

On 11 May, the submarine S-42 located Shima's flagship south-east of New Ireland and sank the Okinoshima with four torpedoes. The following day, submarine S-44 sank the salvage ship Shoei Maru in the same vicinity.

Halsey's TF16 was now located by Japanese air reconnaissance and the decision was made to cancel the third objective of Operation MO. Shima and his battered force was ordered to return directly to Truk. This effectively ended the Battle of the Coral Sea but there were still to be a few ripples.

Nimitz hoped to sink Japanese cripples, in particular the Shokaku, returning from the Coral Sea and several submarines were placed along the expected retirement route. One of these was the Tautog which was en route to Fremantle from Pearl Harbor. Tautog was ordered to proceed to the south of Truk. On 17 May Tautog intercepted and sunk the submarine I-28 which had participated in Operation MO.

The final act of the battle also took place on 17 May when the destroyer Helm, ex TG12.2, found four survivors on a life raft. These were the only survivors from the 68 men that abandoned the Neosho on 7 May.

Summary and Conclusions

Both the Japanese and the Americans believed they had won a major victory. There is a view that the Japanese had tactical success but the Allies won the strategic battle. Ship and aircraft losses were roughly comparable with both sides losing a carrier and a destroyer. While the Lexington was a more valuable ship than the Shoho, other Japanese losses tended to balance the ledger.

At a strategic level, very little had actually changed and neither side had sea control at the conclusion of the battle. While the Port Moresby invasion force had been repulsed it had not been destroyed. The Japanese were to make second assault on Port Moresby in July by way of a land attack over the Owen Stanley Range. The fate of Port Moresby was ultimately to be decided at Kokoda and not in the Coral Sea.

The occupation of Nauru and Ocean islands was eventually completed by the Japanese on 25-26 August. The Japanese foothold at Tulagi was soon extended to the nearby island of Guadalcanal and it was to take six months of savage sea, land and air battles before Guadalcanal was finally secured by the allies.

On its own, the Battle of the Coral Sea was inconclusive. However, if the Coral Sea and Midway battles are viewed as a continuum, then the Battle of the Coral Sea was the first stage of a much larger victory.